The use of polymer slurry as an economic and sustainable way to ...

Exacta

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Universidade Nove de Julho

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Paschoalin Filho, João Alexandre; Guerner Dias, Antonio José; Brum de Lima Duarte, Eric

The use of polymer slurry as an economic and sustainable way to build diaphragm walls – a case

study of a construction work in São Paulo/Brazil

Exacta, vol. 11, núm. 3, 2013, pp. 299-306

Universidade Nove de Julho

São Paulo, Brasil

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299Exacta – EP, São Paulo, v. 11, n. 3, p. 299-306, 2013.

DOI: 10.5585/ExactaEP.v11n3.4562

João Alexandre Paschoalin FilhoProfessor do Programa de mestrado em Gestão Ambiental e Sustentabilidade da Universidade Nove de Julho – Uninove.

São Paulo, SP [Brasil][email protected]

Antonio José Guerner DiasProfessor da Faculdade de Ciências da Universidade do Porto – UP.

Porto, Porto [Portugal][email protected]

Eric Brum de Lima DuarteEngenheiro Construtora W.Torre

Programa de Mestrado Profissional em Gestão Ambiental e Sustentabilidade – GeaS/Uninove

[email protected]

The use of polymer slurry as an economic and sustainable way to build diaphragm walls –

a case study of a construction work in São Paulo/Brazil

Utilização de fluido polimérico como uma forma econômica e sustentável de construção de paredes diafragmas – um estudo de caso de uma obra na

cidade de São Paulo/Brasil

Abstract

The Civil Construction Industry is one of the first economic sectors to react to the stimulus of favorable economic conditions of a country. In such a scenario, new tools for handling and reusing solid waste from construction sites have been extensively discussed in technical conferences. This paper is a case study of a construction work in the city of São Paulo, Brazil where a polymer slurry was used instead of a bentonite-based one as stabilizing fluid for excavation work on diaphragm walls. Based on the evaluation of the data obtained in the cited case study, it was possible to conclude that the use of polymer slurry in the excavation of diaphragm walls is technically and economically feasible, besides presenting several environmental advantages in comparison to the use of bentonite slurry.

Key words: Civil construction industry. Sustainability. Solid waste management.

Resumo

A indústria da construção civil consiste em um dos primeiros setores eco-nômicos a reagir às condições econômicas favoráveis de um país. Neste as-pecto, novas ferramentas de manejo e reuso dos resíduos sólidos produzidos nas obras têm sido extensivamente discutidas em encontros técnicos da área. Este artigo apresenta um estudo de caso de uma obra localizada na cidade de São Paulo, Brasil, em que foi utilizado polímero como fluido estabilizante na escavação de paredes diafragma ao invés de lama bentonítica. Por meio dos dados obtidos por esta pesquisa, foi possível concluir que a utilização de fluido polimérico na escavação de paredes diafragma é técnica e economica-mente viável, além de apresentar diversas vantagens ambientais em relação à utilização de lama bentonítica.

Palavras-chave: Indústria da construção civil. Sustentabilidade. Gestão de resíduos sólidos.

300 Exacta – EP, São Paulo, v. 11, n. 3, p. 299-306, 2013.

The use of polymer slurry as an economic and sustainable way to build diaphragm walls – a case study…

1 Introduction

According to the Brazilian Institute of

Geography and Statistics (IBGE, 2011) the

Brazilian Civil Construction sector showed a

growth rate in 2010 of 11.6% – the best result for

the last 24 years. Furthermore, this sector gener-

ated more than 329,000 formal jobs. It is estimat-

ed that it accounts for investments surpassing U$

45 billion a year. The demand for labor has also

grown accordingly, generating 62 indirect jobs for

every 100 direct jobs.

Nevertheless, although civil construction

has an important social role, helping to directly

reduce the home construction and infrastructure

deficits, which are crucial factors for a country’s

development, it is also responsible for the high

consumption of natural resouces, once most of

the raw material used in construction is extracted

from natural deposits. According to Dias (2004),

around 45% of the resources in Brazil extracted

from nature reserves are utilized in construction.

Although not always obvious for ordinary

citizens, the quantity of waste generated by con-

struction activities represents a highly significant

proportion of urban waste. It is estimated that

construction and demolition waste (CDW) may

account for 50% of the waste generated by some

municipalities in Brazil (ULSEN et al., 2010). In

the city of Salvador (Bahia), CDW represents 45%

of the total volume of urban waste (UW) generat-

ed daily (AZEVEDO et al., 2006), whereas in the

cities of São Paulo (SP) and Rio de Janeiro (RJ) it

is only 21% (GOMES et al., 2008). Morais (2006)

presents data related to a few medium-sized and

large cities in Brazil in which the mass of CDW, as

a percentage, varies from 41% to 70% of the total

mass of urban solid waste.

Currently, it is increasingly common to hear

discussions about sustainability in the construc-

tion industry and about environmental manage-

ment tools for this sector. The concept of sustain-

ability extends beyond practices related to the

preservation of natural resources; it also comprises

several different areas such as sociology, econom-

ics, politics, ecology, culture, and environment, to

name just a few.

Due to the growth in the construction indus-

try and the recognized value of management tools

to reduce its impacts on the environment, sustain-

able processes are becoming increasingly wide-

spread and gaining more relevance in current con-

struction sites. The fact of choosing sustainable

practices to build a facility can affect positively

all the other sectors involved in the construction

process, resulting in lower costs of services and

materials, as well as providing a better quality of

life for the labor force and everyone else who ben-

efits from the building itself.

In building construction there are several

sustainable technologies and products available

in the market that are increasingly being used in

Brazil. The use of polymer as a substitute for ben-

tonite to stabilize excavations in the specific task

of building diaphragm walls could be cited as an

example.

It should be stressed that the practice of

building diaphragm walls is widely used in Brazil,

once most buildings feature several floors which

are below ground level, and that this kind of walls

is needed to resist the thrust of the soil against the

structure and to ensure the stability of the under-

ground floors.

Even though it is more frequently used than

polymers, bentonite slurry causes severe impacts

on the environment, because the waste generated

from its use, besides being a contaminant, is very

difficult to be disposed of. On the other hand, the

polymer has the advantage of being biodegradable,

which makes it easier to dispose of and reduces the

environmental impact caused by the excavation of

the diaphragm wall.

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PASCHOALIN FILHO, J. A.; GUERNER DIAS, A. J.; DUARTE, E. B. L.

The use of a biodegradable product in the

excavation of diaphragm walls presents a profit-

able cost-benefit ratio because it makes it possible

to build according to the technical specifications

of certain environmental cerifications, such as

Leadership in Energy & Environmental Design

(LEED) and AQUA, as well as to lower costs with

the transport and disposal of its waste.

This paper presents a comparative study

between two kinds of products used to stabilize

the excavation of diaphragm walls: bentonite and

polymers. This paper will clarify this issue, as

well as the advantages, disadvantages, costs, and

implementation process, among other relevant in-

formation.

Thus, the present paper intends to show that

the implementation of sustainable practices (such

as the use of polymer slurry), can impact positively

its results, provided they are based on a strategic

planning aligned to the reality of the work, reduc-

ing costs, in addition to lowering its environmen-

tal impact.

2 Building diaphragm walls as contention works

A diaphragm wall can be defined as a vertical

wall with different depths and thicknesses made

of reinforced concrete lamellas that absorb axial

loads, water and soil thrust, and kind of solicitant

efforts. This type of construction is spreading due

to the many advantages that it offers and the vari-

ety of instances in which it can be used.

The process of building a diaphragm wall

can be considered as a relatively simple one, but

to obtain a satisfactory result it is fundamental to

use especific material and equipment as specified

by the Brazilian Technical Standart ABNT: NBR

6122:2010 “Design and construction of founda-

tions” and ABNT: NBR 6118:2007 “Design of

structural concrete - Procedure”.

The building process basically comprises

four distinct steps: (a) building the guide wall; (b)

excavation of the wall; (c) building and placement

of the steel frame and the joint plate; (d) concret-

ing the lamella and excavation of the ground to

get access to the wall; and (e) whenever it is nec-

essary, placement and perforation of the risers.

During the process of building a diaphragm wall

some special equipment is needed, such as a cut-

ting auger, an auxiliary crane, slurry reservoirs,

and suction and injection pumps.

According to Saes et al. (1998), diaphragm

walls present better performance than other kinds

of contention for the following reasons:

a) they can be implemented in almost any

type of terrain without needing to lower the

groundwater table;

b) they form a watertight piece, therefore avoid-

ing the percolation of water into the excavat-

ed ground;

c) they adapt better to the perimeter of the con-

tainment and can be used without any type

of shoring.

As the soil is excavated, the drilling mud is

introduced into the trench and pumped to the

reservatory. The drilling mud efficiency will de-

pend on its physical and chemical properties, that

is, density, viscosity, gel consistency, control of the

filter and plaster, and inhibition of the hydrating

clays (LUMMUS; AZAR, 1986).

Among the drilling muds used to stabilize

excavations, bentonite slurry is the most used.

The purpose of this drilling mud is to counter the

thrust from soil and water, avoiding the collapse

of the faces of the trench during the excavation

work. Bentonite slurry has a stabilizing character-

istic because it forms a layer similar to a gel, called



“cake,” that penetrates into the voids of the soil,

making the wall more uniform and offering better

stability (CARDOSO; SHIMIZU, 2002).

Although the stabilization of perforations us-

ing bentonite slurry is the most commonly-used

method, currently there are several restrictions

to its use by norms from environmental and la-

bor health governmental agencies. In addition to

causing environmental impacts, such as soil con-

tamination, bentonite can also affect the health of

people working directly with this kind of clay.

According to Brazilian Technical Standard

ABNT NBR 10004:2004 “Solid Waste –

Classification”, bentonite slurry is classified as

Class II B Waste – inert and non-hazardous ma-

terial. When it is mixed with soil from an exca-

vation, it must be disposed of on sanitary and/

or industrial landfills where Class II material is

accepted. The waste generated by bentonite slur-

ry makes the soil clog and can cause perishment

of some fauna and flora specimens, generating a

great impact should a large disposal happen in the

same region (MOTA, 2010).

The increasing restrictions imposed on the

use of bentonite slurry by Brazilian environmen-

tal agencies has generated a demand for new tech-

nologies related to the stabilization of excavations.

The use of polymers as substitutes for bentonite is

closely associated to the fact that the polymer is

a biodegradable material, thereby facilitating the

disposal of materials coming from perforations

(MOTA, 2010).

Polymers are classified by Brazilian

Technical Standard ABNT: NBR 10004:2004

as a Class II B Waste – inert and non-hazardous

material, and when they are mixed with the soil

from the excavation, they must be disposed of

on sanitary or industrial landfills where Class

II material is accepted. The treatment applied to

enable the final disposal of the polymer slurry

remaining in the storage tanks is based on the

application of calcium hypochlorite to destroy

the molecular chain of the polymer and of hydro-

chloric acid and/or sodium hydroxide which have

the function of neutralizing the alkalinity of the

slurry, transforming the fluid into residual wa-

ter. After this treatment is applied, the polymer

slurry can be disposed of without harming the

environment (MOTA, 2010).

The Figures 1 and 2 show soil from excava-

tions using bentonite and polymer slurries as drill-

ing muds. The physical aspect of the construction

site and the process of moving and disposing the

excavated soil are very important issues to be con-

sidered for making the best choice.

Figure 1: View of the excavated soil using bentonite slurrySource: The authors.

Figure 2: View of the excavated soil using polymeric slurrySource: The authors.

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Observing the above-shown figures, it is pos-

sible to note that the soil coming from the excava-

tion using bentonite slurry retains a high level of

moisture and is contaminated. This physical state

makes it very difficult to move, transport, and

dispose of the material and impacts negatively on

other services performed at the site. As to the ex-

cavation using the polymer slurry, it is possible to

note that the soil is drier and much easier to move

and does not contain any contaminating agents.

3 Results and discussions

3.1 Characteristics of the studied construction siteThe studied construction site is a commer-

cial building with 16 floors located at President

Juscelino Kubistchek Av. in the city of São Paulo,

Brazil. To create the contention with a diaphragm

wall, it was necessary to excavate 3,344.27 m3 of

soil, equivalent to approximately 4,682.98 tons.

The diaphragm wall has thickness of 0.4 m, depth

of 15 m deep, and surface area of 8,360 m2. Figure

3 shows a view of the construction site.

3.2 Achieved resultsBefore building the diaphragm wall, a study

was performed to identify the best alternative to

attain the stabilization of the excavation that had

to be done. For this purpose, two alternatives

of drilling muds were considered: bentonite and

polymer slurries. The costs were obtained based

on market tenders in São Paulo in 2011 during the

construction process.

The Tables 1 and 2 show the comparison be-

tween the two alternatives that were evaluated for

the present study.

According to Table 1, it can be noticed that

considering the total volume of the soil to be

disposed of, approximately 25% is contami-

nated material, whose total cost for disposal

(including transportation) is 1,17 times superior

to the value of the disposal cost for the non-con-

taminated soil. That said, it can be noticed that

the cost for the disposal of the contaminated

material is 46% of the total cost. Compared to

the alternative using the polymeric slurry, where

the disposed soil is not considered as contami-

nated material, the costs with transportation to Figure 3: General view of the construction siteSource: The authors.

Table 1: Disposal cost of soil using bentonite slurry

Total volume of excavated soil (m3) 3,344.27

Total volume of contaminated soil to be disposed of (m3) 836,07

Total volume of non contaminated soil to be disposed of (m3) 2,508.20

Total cost of non contaminated soil to be disposed of (US$) 53,675.50

Total cost of contaminated soil to be disposed of (US$) 45,983.80

Total cost of the total generated soil to be disposed of (US$) 99,659.35

Source: The authors.

Table 2: Disposal cost of soil using polymer slurry

Total volume of excavated soil (m3) 3,344.27

Total volume of contaminated soil to be disposed of (m3) 0.00

Total volume of non contaminated soil to be disposed of (m3) 3,344.27

Total cost of the total generated soil to be disposed of (US$) 71,567.38




the final disposal site are lower, as can be seen

on Table 2 that follows.

Comparing Tables 1 and 2, it is noticeable

that the disposal of the soil waste generated by

the excavation using polymer slurry is 28% lower

than the cost calculated for the disposal of the soil

when the bentonite slurry is used. This is due to

the fact that the soil resulting from the excavation

using polymer slurry is not considered as contami-

nated material; therefore, it does not require a spe-

cial landfill to be disposed of.

Figure 4 shows the comparison of costs, per

cubic meter, for both alternatives.

Figure 3 shows that the cost for the disposal

per volume of material corresponds to US$29.80

for the bentonite slurry option and to US$ 21.4

for the polymer slurry. The mass of studied drill-

ing muds needed for the excavation of the stud-

ied diaphragm wall has also been estimated. The

quantity was obtained through the information

provided by the manufacturers of the used drill-

ing muds and by the ratio of utilization verified

at the construction site. The estimated values are

presented in Table 3.

On Table 3, it can be seen that, considering

the volume of excavation needed for the construc-

tion work, the consumption of bentonite clay was

18 times higher than the consumption of polymer.

The study also contemplated the costs comprised

in the construction of the diaphragm wall using

bentonite and polymer slurries. The calculation

included the values related to the use of the stud-

ied drilling muds, the total cost of the mechanized

excavation of the wall, and the transportation and

disposal cost of the waste generated by the exca-

vation work. The costs related to the diaphragm

wall steel frame were not included. The values are

presented on Tables 4 and 5.

Considering Tables 4 and 5, it is possible to

point out that the estimated costs present a dif-

ference of approximately 6%, when the values for

the bentonite and polymer slurries are compared,

Figure 4: Comparison of the cost for disposal (US$/m3)Source: The authors.

Table 3: Estimated consumption for bentonite and polymer slurries

Volume of the excavation (m3) 3,344.27

Mass of polymer to be used (kg) 2,006.50

Mass of bentonite clay to be used (kg) 35,783.70


Table 4: Cost estimated to build diaphragm wall using bentonite slurry


Total cost for excavation works (US$) 309,345

Transportation and disposal cost (US$) 99,659.40

Total cost of applying bentonite slurry (US$) 14,923.30

Total estimated cost (US$) 423,986.70


Table 5: Cost estimated to build diaphragm wall using polymer slurry


Total cost for excavation works (US$) 309,345

Transportation and disposal cost (US$) 71,561.40

Total cost of applying polymer slurry (US$) 74,978.50

Total estimated cost (US$) 455,890.90


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amounting to US$ 31,904.42. It should also be

pointed out that even presenting a cost five times

lower than that of the bentonite slurry, the cost

of the transportation and disposal of its waste is

much higher than for the polymer slurry. Figure 5

presents a comparison between the costs for both

alternatives presented per area of diaphragm wall

to be built.

Figure 5 shows the difference in the cost per

area to build the studied diaphragm wall; the

comparison reveals a difference of approximately

U$4.00/m2 between the two solutions analyzed

so far.

4 Conclusions

Based on the parameters obtained by the

present research, the following conclusions can be

presented:

a) Civil construction is a very important eco-

nomic sector in Brazil, being responsible for

generating jobs and income and for reduc-

ing the country’s housing and infrastructure

deficits. Nevertheless, civil construction is

also responsible for the generation of a great

volume of solid waste. Therefore, it is very

important to adopt systems of environmental

management at construction sites, with the

main goal of reducing the quantity of solid

waste, as well as lowering both losses dur-

ing the construction process and the need for

natural raw material.

b) The data that were obtained indicated that

the use of polymer slurry as a drilling mud

provided an economical alternative, even

though it is a little more expensive (6%) than

bentonite slurry, due to the environmental

advantages it offers. Being a biodegradable

product is a relevant aspect due to the envi-

ronmental issues that are increasingly being

faced by the construction industry; and in

the case of the use of the polymer slurry, it

was possible to reduce the quantity of exca-

vated soil that needed to be disposed of and

transported. In addition to this, for the same

volume of soil to be excavated, the amount

of material consumed was lower compared to

what was needed if using bentonite slurry. It

is important to highlight that the implemen-

tation of practices and the use of products

that cause a low environmental impact, such

as the use of polymer slurry, is one of the re-

quirements to be met for a construction site

to get Green Building certifications, such as

LEED and AQUA.

ReferencesABNT – Associação Brasileira de Normas Técnicas. NBR 6122: Projeto e execução de fundações. Rio de Janeiro, 91 p., 2010.

ABNT – Associação Brasileira de Normas Técnicas. NBR 6118: Projeto de Estruturas de concreto. Rio de Janeiro, 221p, 2007.

Figure 5: Comparison of the costs per area for both drilling mudsSource: The authors.



ABNT – Associação Brasileira de Normas Técnicas. NBR 10004: Resíduos sólidos – Classificação. Rio de Janeiro, 48 p.,2004.

AZEVEDO, G. O.; KIPERSTOK, A.; MORAES, L. R. Resíduos da construção civil em salvador: os caminhos para uma gestão sustentável. Engenharia Sanitaria e Ambiental, v. 11, n. 1, p. 65-72, 2006.

CARDOSO, F. F. E.; SHIMIZU, J. Y. Sistemas de contenção. Apostila DepartamentodeEngenhariaeConstruçãoCivil,Escola Politécnica da Universidade de São Paulo, São Paulo, p. 285, 2002.

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MORAIS, G. M. D. Diagnóstico da deposição clandestina de resíduos de construção e demolição em bairros periféricos de Uberlândia: subsídios para uma gestão sustentável. 2006. 220p Dissertação (mestrado)–Faculdade de Engenharia Civil, Universidade Federal de Uberlândia, Uberlândia, 2006.

SAES, J. L.; HACHICH, W.; FALCONI, F. F. Fundações: teoria e prática. São Paulo: Pini. 452 p., 1998.

ULSEN, C. et al. Composição química de agregados mistos de resíduos de construção e demolição do Estado de São Paulo. Revista da Escola de Minas, v. 63, n. 2, p. 339-346, 2010.

Recebido em 14 out. 2013 / aprovado em 6 dez. 2013

Para referenciar este texto PASCHOALIN FILHO, J. A.; GUERNER DIAS, A. J.; DUARTE, E. B. L. The use of polymer slurry as an economic and sustainable way to build diaphragm walls – a case study of a construction work in São Paulo/Brazil. Exacta – EP, São Paulo, v. 11, n. 3, p. 299-306, 2013.

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